1. Field of the Invention
The present invention relates to a solid-state imaging device having a scanning circuit and a photoconductive film formed in layers on a semiconductor substrate.
2. Background Art
In order to obtain a high photosensitivity, a conventional solid-state imaging device with a multi-layered structure employs a photoconductive film made of amorphous silicon placed on a scanning circuit substrate. The scanning circuit on the substrate may be of a type such as MOS (metal-oxide-silicon), CCD (charge-coupled device) or BBD.
However, one problem with the conventional multi-layered solid-state imaging device is that the sheet resistivity of the amorphous silicon used as a photoconductive material is slightly lower than that of the other materials. This relative resistivity causes a significant reduction in resolution and increases the chance of color mixing. This problem can be eliminated by increasing the sheet resistivity of the amorphous silicon film. However, in this case, carrier mobility is decreased or the trap density is increased, producing an after-image of greater intensity.
Another approach is to isolate the picture elements (pixels) in the photoconductive film by, for instance, oxide regions. However, the process of fabricating such an isolated solid-state imaging device needs an extra step for the minute processing. Therefore, the number of fabricating steps is increased, as a result of which cost becomes high.